The industry of semiconductor manufacturing involves highly complex techniques for integrating circuits into semiconductor materials. Multiple fine layers of metals and materials form these integrated circuits. To increase the speed and performance of devices utilizing integrated circuits, the size of semiconductor devices must be decreased. Due to the large scale of circuit integration and the decreasing size of semiconductor devices, the semiconductor manufacturing process is prone to processing defects. When the dimensions of semiconductor devices are decreased, the thickness of the various layers of metals and materials must be controlled more and more accurately. As semiconductor device film layer thickness approaches a few atomic levels, existing techniques for monitoring and measuring this dimension become very challenging due to measurement sensitivity scale. For example, measuring the thickness of a sheet of paper with a scale no finer than an inch is next to impossible; the difference in scale is too great to make a meaningful and accurate measurement.
Testing procedures and measurement scale are therefore critical to maintaining quality control and accurately testing and measuring semiconductor devices. Because the testing procedures are an integral and significant part of the manufacturing process, the semiconductor industry constantly seeks more accurate and efficient testing procedures. Increasingly, this requires seeking testing procedures that are accurate and efficient at extremely small dimensions.
There are several methods currently used to characterize thin dielectric films. For example, scanning force microscopes are known in the art. U.S. Pat. No. 5,902,928 to Chen et al., entitled, “Controlling Engagement of a Scanning Microscope Probe with a Segmented Piezoelectric Actuator,” discloses a scanning probe microscope that includes a segmented piezoelectric actuator having a course segment and a fine segment, the outputs of which are combined to determine the movement of a distal end of the actuator, to which the probe is mechanically coupled.
In U.S. Pat. No. 6,318,159 to Chen et al., entitled, “Scanning Force Microscope with Automatic Surface Engagement,” the vibrating probe of a scanning force microscope is brought into engagement with a sample surface in an initial approach process moving the probe toward the sample surface until the amplitude of probe vibration at an excitation frequency is measurably affected by forces between the tip and the sample, and then in a final approach process in which a change in vibration amplitude caused by a dithering vibration superimposed on the excitation vibration exceeds a predetermined threshold limit. During approach and scanning, vibration amplitude is measured through a demodulator having an intermediate reference signal locked in phase with the tip motion signal.
U.S. Pat. No. 5,065,103 to Slinkman et al., entitled, “Scanning Capacitance—Voltage Microscopy,” discusses an apparatus and method for generating microscopic scan data of C-V and/or dC/dV over a scan area. A scanning microscope is provided with a voltage biased tip that is scanned across an area to derive the data and the data can then be used to derive a plot of semiconductor dopant level across the scan area.
A method for mapping a mechanical property of a surface of a sample with a scanning force microscope is described in U.S. Pat. No. 5,700,953 to Hlady et al. The method comprises the steps of: (a) scanning a fine tip supported on a cantilever beam in contact with the surface of a sample; (b) applying a loading force on the surface of the sample by the fine tip; (c) oscillating the cantilever beam relative to the surface of the sample; (d) measuring a detector response of the fine tip; (e) determining the amplitude and a change in phase angle of the detector response; and (f) relating the amplitude and the change in phase angle to a property of the surface of the sample.
A “Scanning Capacitance Microscope” is described in U.S. Pat. No. Re. 32,457 to Matey. Variations in topography and material properties of the surface layer of a body are observed in microscopic imaging using a scanning capacitance probe.
Mazur et al., discloses a “Non-Invasive Electrical Measurement of Semiconductor Wafers,” in U.S. Pat. No. 6,492,827. A semiconductor wafer probe assembly includes a chuck assembly configured to receive a back surface of a semiconductor wafer and an electrical contact for contacting the semiconductor wafer. A probe having an elastically deformable conductive tip is movable into contact with a semiconducting material forming a front surface of the semiconductor wafer or with a front surface of a dielectric formed on the front surface of the semiconducting materials. A tester is connected for applying an electrical stimulus between the electrical contact and the conductive tip for measuring a response to the electrical stimulus and for determining from the response at least one electrical property of the semiconducting material and/or the dielectric.
U.S. Pat. No. 6,172,506 to Adderton et al., entitled, “Capacitance Atomic Force Microscopes and Methods of Operating Such Microscopes,” discloses scanning a surface of a sample in intermittent contact mode with an atomic force microscope where the probe tip is electrically conductive and is electrically connected to a capacitance sensing circuit. The oscillation of the atomic force microscope probe modulates capacitance between probe tip and sample surface and the modulated capacitance is demodulated to yield the capacitance properties of the sample.
Other methods for characterizing thin dielectric films are also known in the art. In U.S. Pat. No. 6,459,280 to Bhushan et al., capacitive film thickness measurement devices and measurement systems are described, including a device and technique for determining film thickness by suspending the film in a liquid dielectric. U.S. Patent Application Pub. No. 2002/0130674, discloses a steady state method for measuring the thickness and the capacitance of ultra thin dielectric in the presence of substantial leakage current. U.S. Pat. No. 6,388,452 to Picciotto, entitled, “Device for Sensing Media Thickness Using Capacitance Measurements,” discloses deriving the thickness of a media by electronically measuring the capacitance between the first and second electrodes of a variable capacitance capacitor. U.S. Pat. No. 6,465,267 to Wang et al., describes a “Method of Measuring Gate Capacitance to Determine the Electrical Thickness of Gate Dielectrics,” by connecting a meter to an integrated circuit gate structure and an active region located proximate the integrated circuit gate structure, applying forward body bias to the transistor at a gate inversion measuring point, and measuring capacitance from the meter while the transistor receives the forward body bias. U.S. Pat. No. 6,445,194 to Adkisson et al., describes a “Structure and Method for Electrical Method of Determining Film Conformality,” and, in particular, for measuring the sidewall deposition thickness of dielectric films.
There are several drawbacks associated with the methods of the prior art. It is frequently difficult to obtain consistent measurement data. The probe methods of the prior art often are not highly sensitive, requiring a larger contact area that increases the chance of damaging the sample and also reduces the accuracy of the measurements. In addition, scanning capacitance microscopes are often sensitive to the change of capacitance when stimulated with an ac bias, i.e., dC/dV.
In light of the foregoing, a capacitance probe for thin dielectric film characterization that is highly sensitive and obtains consistent measurement data is desirable.